1. Field of the Invention
The present invention relates to a liquid crystal projector, in particular, to that in which is applied to a technology for protecting a liquid crystal panel from an increase in the temperature thereof.
2. Description of Prior Art
Conventionally, it is common that a liquid crystal projector is heated by light irradiated for projecting an image of a liquid crystal panel, thereby increasing the temperature thereof. For suppressing the increase in the temperature, cooling air is sent onto the liquid crystal panel by means of a fan. Thereby, generation of deformation in the liquid crystal panel, etc., due to the increase of the temperature is prevented.
Such protection technology of the liquid crystal panel is already disclosed and known by, for example, Japanese Patent Laying-Open No. Hei 4-60533 (1992) and Japanese Patent Laying-Open No. Hei 4-60534 (1992). In Japanese Patent Laying-Open No. Hei 4-60533, it is constructed by comprising a detection means of surrounding temperature which is positioned in the vicinity of the liquid crystal panel, a wind velocity detection means (or sensor) for detecting wind velocity of the cooling air at an incident side with respect to the liquid crystal panel, and a means for detecting the lamp energy of a light source. An output of the surrounding temperature detection means is sent a micro-computer, thereby if the output which is sent to is higher than a preset upper limit value, then it turns OFF an electric power source, and if it is lower than that an information is sent to a control circuit. Also, the output of the wind velocity detection means is sent to the micro-computer, thereby if the wind velocity is less than a preset value due to clog in a filter, etc., then it turns OFF the electric power source, and if it is greater than the preset value, an information is sent to the control circuit. Furthermore, an output of the means for detecting the lamp energy is also sent to the micro-computer, thereby if the energy is less than a preset value, it indicates an exchange of the lamp, and if it is greater than the preset value, an information is sent to the control circuit. On a basis of the information of the surrounding temperature of the panel, of the wind velocity at the incident side, and of the lamp energy, which are sent to the control circuit, the revolution numbers of a suction fan and an exhaustion fan are controlled so that the temperature of the liquid crystal panel is less than a predetermined constant value.
With the conventional art mentioned in the above, the wind velocity sensor is positioned at a downstream side of an air flow of the cooling air passing through the liquid crystal panel and the exhaustion fan is positioned at a rear side of the liquid crystal panel, therefore causing following problems. For instance, if the clog or the like is caused in a suction system including the suction fan due to any reason, the cooling air by the suction fan is reduced down in the amount of wind as well as in the velocity thereof, however, due to an affect of the air flow formed by the exhaustion fan, the wind velocity which is detected by the wind velocity sensor will not decrease down greatly, therefore it is likely to fail to detect the decrease in the wind amount by the suction fan so that the temperature of the liquid crystal panel rises up.